1. Field of the Invention
The present invention relates to a transmission device, a transmission method, a reception device, and a communication system, and particularly relates to a transmission device, a transmission method, a reception device, and a communication system whereby wiretapping by a third party can be prevented by increasing the error rate of a reception signal to ½ even in the case of a minute interference signal being included.
2. Description of the Related Art
Code has been known as a method for enhancing the confidentiality of information with a predetermined communication path. Code is classified roughly into classic code not employing a key for encryption and decryption (deciphering), and modern code employing a key. Further, the modern code employing a key is classified roughly into the common key encryption system employing a common key, and the public key encryption system employing a public key. As for the common key encryption system, for example, DES, Triple DES, AES, and so forth have been known, and as for the public key encryption system, for example, RSA, and so forth have been known (e.g., see RFC2313, IETF (The Internet Engineering Task Force), Internet <URL:http://www.ietf.org/rfc/rfc2313.txt?number=2313>, and RFC3268, IETF (The Internet Engineering Task Force), Internet <URL:http://www.ietf.org/rfc/rfc3268.txt?number=3268>).
With the common key encryption system, the transmission side and reception side have a common key, and the transmission side encrypts information using this common key to transmit this, and the reception side decrypts the encrypted information using the common key. Accordingly, the common key encryption system is a system for preventing the others (malicious third party) from deciphering information by only the transmission side and reception side sharing the common key.
On the other hand, with the public key encryption system, the reception side possesses a secret key, and also a public key generated from the secret key is provided to the transmission side. The transmission side encrypts information using the public key to transmit this, and the reception side decrypts the encrypted information using the secret key. Accordingly, the public key encryption system is a system for preventing the others from deciphering information by employing a public key difficult to assume its secret key.
With either the common key encryption system or public key encryption system, in order to subject information to confidentiality in a more secure manner, it becomes important how the transmission side and reception side can share the key information in a secure manner. For example, it is desirable to ensure a dedicated secure communication path in the case of providing the key information to the other party, but actually it is difficult to ensure such a communication path. Also, it is more difficult to ensure the dedicated communication path whenever the key information is updated.
Also, using the same communication path as a communication path for transmitting ordinary information leads to a problem since only the same safety as to the transmitted key information as the safety as to information not encrypted can be ensured.
Thus, it is difficult for only a sending person and receiving person to share the key information in a secure manner, and even if the sending person and receiving person can share the key information, the key information may be stolen with certain means in some cases.